[1] Nord Trondelag Hosp Trust, Levanger Hosp, Dept Med & Rehabil, Levanger, Norway
[2] Norwegian Univ Sci & Technol NTNU, Fac Med & Hlth Sci, HUNT Res Ctr, Dept Publ Hlth & Nursing, Forskningsveien 2, NO-7600 Levanger, Norway
[3] Trondheim Reg & Univ Hosp, Clin Thorac & Occupat Med, St Olavs Hosp, Trondheim, Norway
[4] Norwegian Univ Sci & Technol NTNU, Fac Med & Hlth Sci, KG Jebsen Ctr Genet Epidemiol, Dept Publ Hlth & Nursing, Trondheim, Norway
[5] Univ Bristol, MRC Integrat Epidemiol Unit, Bristol, Avon, England
[6] Norwegian Univ Sci & Technol NTNU, Fac Med & Hlth Sci, Dept Publ Hlth & Nursing, Trondheim, Norway
[7] Gothenburg Univ, Sahlgrenska Univ, Hosp & Inst Med, COPD Ctr, Gothenburg, Sweden